1. Field of the Invention
The present invention relates to a hybrid type stepping motor having eight (8) stator poles equiped with four (4)-phase connected windings.
2. Description of the Prior Art
In the conventional hybrid type stepping motor in which the exciting field is switched phase by phase, the stepping angle .theta..sub.s can be represented by EQU .theta..sub.s =360.degree./2.multidot.n.multidot.Z.sub.R
where n is the number of phases and Z.sub.R is the number of teeth of the rotor. Futhermore, the load angle .theta..sub.L at the maximum torque is determined by the number of teeth (Z.sub.R) and can be represented by EQU .theta..sub.L =360.degree./4.multidot.Z.sub.R
Therefore, a relation .theta..sub.L =k.multidot..theta..sub.s is established between the step angle .theta..sub.s and the load angle .theta..sub.L where k is a constant. In this case, in order to make possible to accelerate or decelerate the motor at a high rate without misstepping, the constant k should be as larger than 1 as possible.
Since the conventional hybrid type stepping motor having 8 stator poles is usually provided with 2-phase connected windings, the step angle .theta..sub.s is 360.degree./4.multidot.Z.sub.R and thus a relation .theta..sub.L =.theta..sub.s (k=1) is established between the two angles. Therefore, when it is desired to use that motor in a high speed range, it is difficult to set the rise time and the fall time for the slow-up and slow-down motions, and, further, there is the turbulence or hunting phenomenon in some specific input frequency range.